In recent years there has developed an increased demand for ultra high purity oxygen for use, for example, in the electronics industry for the production of semiconductors and microchips.
Oxygen having a high purity of about 99.5 percent has long been produced by the cryogenic rectification of air in a double column cryogenic rectification plant. Heretofore, this conventional oxygen product has been used for production of ultra high purity oxygen by upgrading to a purity of 99.99 percent or more.
In some instances only a small amount of ultra high purity oxygen is required without the need for conventional high purity oxygen. In these situations, a conventional double column system would produce excessive amounts of oxygen and thus be wasteful. Furthermore, nitrogen product may be required at an elevated pressure. Since the conventional double column system produces nitrogen at a low pressure, further compression of the nitrogen product would be required further adding to the inefficiency of the conventional double column cycle for such situations.
It is known that nitrogen, including elevated pressure nitrogen, may be produced by the cryogenic rectification of air employing a single column system. It would be desirable to have a single column system which can efficiently produce nitrogen, including elevated pressure nitrogen, by the cryogenic rectification of air, which can be readily integrated with a system for producing ultra high purity oxygen without harming the efficiency of the single column nitrogen production system.
Accordingly, it is an object of this invention to provide a cryogenic rectification system for producing nitrogen and ultra high purity oxygen wherein the nitrogen product is produced in a single column system.